This invention relates to video display systems, methods of operating such systems to prevent damage to their high intensity discharge lamps during cool down periods, and to computer readable media comprising instructions for implementing the method and operating the system.
Liquid crystal micro displays (LCD) and liquid crystal on silicon (LCOS) television (TV) receiver projection systems often use a high-intensity discharge lamp, or bulb, as a light source. Typical high intensity discharge lamps operate with mercury vapor. It is known that preventing the mercury vapor from de-energizing before re-striking the vapor (i.e., turning power to the lamp back on immediately after or shortly after turning the power-off) can shorten the bulb life.
Because re-energizing a partially energized bulb should be avoided, some projection systems introduce a restart delay feature. Such a feature prevents the user from turning the TV receiver back on until the bulb is fully de-energized, which typically occurs after approximately 30 seconds. This approach is particularly annoying to the user because the user is not able to turn the TV receiver back on immediately, as is possible in a TV receiver that does not use such a high-intensity discharge lamp. Instead, the user must endure a start-up delay. The start-up delay includes approximately 30 seconds for the bulb to cool down and approximately another 30 seconds for the bulb to reheat.
In response to a user's command requesting system turn off, some systems display a message asking “Do you really want to turn off the system?” Such systems are useful for avoiding unintentional shutdowns, but do not solve the problem of intentional shutdowns followed shortly by intentional attempts to turn the system on.
Other prior systems give a false appearance of being turned off but maintain the bulb powered or energized during an interval of, for example, 30 seconds following a power-off command and if the user issues a power-on command before that interval has elapsed, the user does not experience any start-up delay and the television display resumes without having turned off the bulb.
Certain other prior art systems enforce the lamp cool down period by blinking the Power LED for a few seconds upon receipt of the Power-on command. However, the power-on command is then discarded. This results in frustration to the user because the user has no feedback on the precise duration of the cool down period and must resort to repeated attempts to power-on the television until at last it responds.